Method of brazing using a ductile low temperature brazing alloy

ABSTRACT

Titanium-silver alloys containing specified amounts of silver and titanium and controlled amounts of copper, aluminum and mixtures thereof are suitable for brazing ceramics, other non-metallic and metallic materials. These alloys also may contain controlled amounts of tin, palladium, indium and mixtures thereof.

This application is a continuation of application Ser. No. 757,962 filedSept. 20, 1984 which is a continuation of 394,226 filed July 1, 1982,now abandoned.

FIELD OF INVENTION

This invention relates to brazing alloys. More particularly it relatesto low temperature brazing alloys containing titanium.

BACKGROUND

An alloy foil sold under the trademark of Ticusil by the Wesgo Divisionof GTE Products Corporation, Belmont, Calif. contains 4.5% by weight oftitanium, 68.8% by weight of silver and 26.7% by weight of copper. Thiscomposite alloy, while having the ability to wet various ceramicmaterials and has a relatively low brazing temperature, is not ductileand can not be rolled to a foil in a satisfactory manner and uponbrazing contains a brittle dispersed phase.

Other titanium containing alloys containing higher amounts titanium areknown to wet ceramics. These can be made into a ductile foil form byrapid solidification techniques, however, upon brazing will form a jointcontaining a brittle dispersed phase.

SUMMARY OF THE INVENTION

Reactive metal-silver alloys containing specified amounts of silver anda reactive metal and controlled amounts of copper or aluminum ormixtures thereof also have liquidus temperatures in the range of fromabout 750° C. to about 950° C. are ductile and after brazing arerelatively free of hard dispersed phases. These alloys also may containas optional ingredients controlled amounts of tin, palladium, indium andmixtures thereof.

DETAILS OF PREFERRED EMBODIMENTS

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above description of some of the aspects of the invention.

Within the context of this application the term "reactive metal" meanstitanium, vanadium, zirconium and mixtures thereof.

The amount of the reactive metal in a reactive-silver alloy containingcopper or aluminum or mixtures thereof can not appreciably exceed 4% byweight and achieve a ductile material which upon brazing is free ofdispersed phases. Table I below shows the effect upon hardness andductility of various Ti-Ag-Cu alloys.

                  TABLE I                                                         ______________________________________                                                                      Knopp                                           % Titanium                                                                             % Ag      % Cu       Hardness                                        (by weight)                                                                            (by weight)                                                                             (by weight)                                                                              50 g   Ductility                                ______________________________________                                        0        72        28         140    ductile                                  .5       71.6      27.9       140    ductile                                  1.0      71.3      27.7       145    ductile                                  3.0      69.8      27.2       140    ductile                                  4.0      69.1      26.9       130    ductile                                  4.5      68.8      26.7       201(M) cracks                                                                 664(D) 2 phases                                 5.0      68.4      26.6       190(M) cracks                                                                 530(D) 2 phases                                 ______________________________________                                         M = Matrix                                                                    D = Dispersed Phase                                                      

As can be seen from the data in Table I about 4% by weight of titaniumis the upper weight limit on the amount of titanium that can be presentin the Ti-Ag-Cu alloy system and achieve ductility. Similar results uponductility are achieved when the Ag-Cu ratio changes from the 72% Ag-28%Cu eutectic. Additionally similar ductility results are achieved in theTi-Ag-Al system.

When vanadium or zirconim or mixtures thereof is the reactive metal thematerial is not as ductile as when titanium is the reactive metal. Thepresence of brittle dispersed phases relates to the level of thereactive metal and is independent of the particular reactive metal used.When the reactive metal content is above about 2% by weight whenvanadium, zirconium or mixtures thereof are used, rapid solidificationmanufacture techniques or intermediate annealing is required to producea ductile foil. Titanium is the preferred reactive metal.

In many brazing applications it is desired to utilize relatively lowbrazing temperatures, that is the liquidus of the alloy should be in the600° C. to 950° C. range thus the lower brazing temperatures can beutilized. If desired, in addition to the titanium-silver-copper oraluminum or mixtures of Cu and Al, additional metals of tin, palladium,indium or mixtures thereof can be included as optional ingredients.

While the liquidus temperature is in the ranges specified, the flowtemperature, that is the temperature at which the alloys of thisinvention flow and wet the materials to be brazed is important inutilizing the materials using conventional brazing techniques. If thematerials to be brazed can withstand about 900° C., it is preferred toutilize brazing temperatures in excess of 900° C. even if the particularbrazing alloy has a lower liquidus temperature. The flow temperaturesfor the products of this invention generally range from about 900° C. toabout 1050° C.

The amount of reactive metal in the alloys is from about 0.25% by weightto about 4% by weight with from about 1.0% by weight to about 2% byweight being preferred. That amount of silver is from about 20% byweight to about 98.75% by weight. It is preferred that the silvercontent be between about 60% by weight and about 75% by weight.

When copper and aluminum are present in the alloy, the weight percent ofthese elements can vary from about 1% by weight to about 70% by weight,however, the relative amounts of silver and copper, aluminum or mixturethereof, along with the optional ingredients of tin, palladium andindium are adjusted to achieve a liquidus temperature within the rangeof from about 600° C. to about 950° C. In the Ti-Ag-Cu system withoutother metals present it is preferred that the eutectic having a weightratio of Ag:Cu of about 72:28 be employed. The preferred copper weightrange therefore varies from about 20% by weight to about 40% by weight.The preferred aluminum content is from about 4% by weight to about 10%weight.

The optional second metal additions include tin, palladium, indium andmixtures thereof. These metal additions can vary from about 1% by weightto about 30% by weight of the alloy. When tin is utilized it ispreferrably added the weight range of from about 3% by weight to about15% weight. When palladium is utilized, the preferred amount ofpalladium is from about 5% by weight to about 25% by weight. When indiumis utilized, the preferred amount is from about 2% to about 15% byweight.

To more fully illustrate the subject invention the following detailedexamples are presented. All parts, percentages and proportions are byweight unless otherwise indicated.

EXAMPLE I

Four alloys containing about 1%, 2%, 3% and 4% titanium are preparedusing skull melting equipment and a base alloy of the 72% silver-28%copper eutectic. These four alloys are rolled down to a workable,ductile, 5 mil thick foil.

A portion of each of the foils is placed between two pieces of 97%alumina ceramic which are 3/4" wide by 11/2" long by 0.025" thick. Thesefour samples are brazed at about 920° C. at 10⁻⁵ mm Hg for about 5minutes. Suitable brazed joints are achieved with all four alloys.

EXAMPLE 2

An alloy containing about 2% titanium, about 59% silver, about 29%copper and about 10% tin is prepared and rolled to a foil having athickness of about 10 mils. The foil is workable and ductile and is usedto braze alumina, as in Example 1, except that a brazing temperature ofabout 900° C. is used. A suitable brazed joint is exhibited.

EXAMPLE 3

An alloy containing about 2% titanium, about 67% silver, about 26%copper and about 5% palladium is prepared and rolled to a foil having athickness of about 4 mils. The foil is cut into a 1/4 inch wide ribbonand a piece of this ribbon is placed between a piece of metallic alloycontaining about 53.8% iron, 29% nickel, 17% cobalt and 0.2% manganeseknown as Kovar and a piece of 97% alumina. The dimension of the Kovarare about 1/2" wide by about 3/4" by 0.010" thick. The dimensions of thealumina are about 1/2" wide by about 3/4" long by about 0.030" thick.The Kovar, brazing foil and alumina assembly is heated to about 1020° C.under about 10⁻⁵ mm Hg pressure for about 10 minutes. The brazed jointis sound.

EXAMPLE 4

An alloy containing about 3% titanium, about 4.5% aluminum and about92.5% silver is prepared by convention powder metallurgy techniques. Afoil having a thickness of about 4 mils is prepared using anintermediate vacuum anneal. When placed between two pieces of 97%alumina and brazed at about 1050° C. at 10⁻⁵ mm Hg for about 10 minutes,a suitable brazed joint is formed.

EXAMPLE 5

Following the procedure given in Example 4, an alloy containing about0.5% titanium, about 10% indium, about 24.5% copper and about 65% silveris prepared in the form of a foil. The foil having a thickness of about6 mils is suitable for brazing copper to alumina using a brazingtemperature of about 850° C. at 10⁻⁵ mm Hg pressure and a time of about10 minutes.

EXAMPLE 6

Silicon nitride solde under the tradename of SNW-1000 by the WesgoDivision of GTE Products Corporation, Belmont, Calif. is satisfactorilybrazed to mild steel at a brazing temperature of about 920° C. at 10⁻⁵mm Hg pressure using a brazing foil of about 3 mils thickness and havingcomposition of about 2% titanium, about 27.4% copper and about 70.6%silver.

EXAMPLE 7

The following alloys are prepared as in Example 1.

    ______________________________________                                        72% Ag - 28% Cu                                                                            99.0%   98.0%     97.0% 96.0%                                    Ti           0.5%    1.0%      1.5%  2.0%                                     Zr           0.5%    1.0%      1.5%  2.0%                                     ______________________________________                                    

The rolled foil is placed between two alumina substrates and brazed. Theuse of Ti Zr 1:1 ratio shows reduced flow temperature compared to Tialloy and flows at 880° C.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein with out departing from the scope of the invention as defined bythe appended claims.

What is claimed is:
 1. The method of joining silicon nitride to anotherpart by brazing comprising the steps of:preparing a brazing alloycomposition consisting essentially of 20 to 98.75 weight percent silver,20 to 40 weight percent copper, and 0.25 to 4 weight percent titanium,said composition having a liquidus temperature in the range from about750° to 950° C.; rolling the brazing alloy composition down to a thinfoil; disposing brazing alloy in said thin foil form between an assemblycomprising the silicon nitride and the part to which the silicon nitrideis to be brazed; and heating said assembly in vacuum to a temperature atwhich the foil melts, thereby brazing the silicon nitride to said part.2. The method of joining silicon nitride to a mild steel part by brazingcomprising the steps of:preparing a brazing alloy composition consistingof 70.6 weight percent silver, 27.4 weight percent copper, and 2 weightpercent titanium, said composition having a liquidus temperature in therange from about 750° to 950° C.; rolling the brazing alloy compositiondown to a 3 mil thick foil; disposing brazing alloy in said foil formbetween an assembly comprising the silicon nitride and a mild steel partto which the silicon nitride is to be brazed; and heating said assemblyin vacuum at about 920° C. thereby brazing the silicon nitride to themild steel part.